|
Oceanic whitetip sharks, once the most common shark in the world, are almost completely extinct, according to a new census in the Gulf of Mexico. Over the past 50 years, their numbers have crashed by more than 99% in the Gulf. Researchers think the same drop has happened around the world.
"What's shocking is that nobody noticed until now," says Julia Baum of Dalhousie University in Halifax, Canada, who took part in the analysis**. Her colleague Ransom Myers says the situation is akin to herds of buffalo disappearing from the US Great Plains without anyone noticing.
The study adds to a body of work that points to a massive decline in numbers of large predator species in the oceans. Baum and Myers previously found that silky sharks in the Gulf of Mexico have declined by around 90% since the 1950s. And hammerhead shark numbers in the Atlantic have plummeted by 89% in the past 15 years *†. "Sharks are in a global extinction crisis," says Myers. "Wherever you look around the world the story is the same.” But the case of the oceanic whitetip is particularly dramatic, he says.
Baum and Myers blame tuna fishing and the lucrative trade in shark fins for the animals' demise. Shark's fin soup is a prized delicacy in many regions - in Hong Kong's markets, for example, a kilogram of shark fin can fetch hundreds of dollars.
The sharks are often hooked on the long lines used to catch tuna, Myers explains. Although US law prevents fishermen from cutting off the sharks' fins, the practice is rife in many areas of the world. "It's very difficult for poor fishermen to resist catching them," Myers says.
Myers is calling for a worldwide ban on shark-finning. Canada, Australia and the United States have outlawed the practice, but proposals for a similar law in the European Union have not yet passed. The World Conservation Union (IUCN) is spearheading a campaign for countries to recognize the damage caused by the trade in shark fins.
Ernest Hemingway wouldn't have been able to catch marlin without them being covered by shark bites ~ Ransom Myers - Dalhousie University, Canada
Lack of data
The crisis may not have been noticed before simply because of a lack of data. Myers found a government survey of the number of whitetip sharks accidentally caught on tuna fishing lines in 1954 in the Gulf of Mexico. No further record was kept of the sharks’ numbers until 1992, mainly because the sharks weren’t being intentionally fished in the Gulf.
Baum and Myers compared the few surveys that do exist, and found that the sharks were vastly more abundant in the 1950s than they are today.
They were so common, in fact, that they were viewed as pests by fishermen. "Ernest Hemingway wouldn't have been able to catch marlin without them being covered by shark bites," says Myers.
It seems that oceanic whitetips may even have been the most common large animal in the world. "They were the dominant species of the world's largest ecosystem," says Myers. "The fact that they disappeared without us noticing is amazing."
References
**Baum, J. K. & Myers, R. Shifting baselines and the decline of pelagic sharks in the Gulf of Mexico. Ecology Letters, 7, 135 - 145, doi:10.1111/j.1461-0248.2003.00564 (2004).
*†Baum, J. K. et al. Collapse and conservation of shark populations in the Northwest Atlantic. Science, 299, 389 - 392, (2003).
Top
|
